Novel Bipolar Indole-Based Solution-Processed Host Material for Efficient Green and Red Phosphorescent OLEDs

A new bipolar host material 2-(2′-(5-(dibenzo[ b, d ]furan-4-yl)-1 H -indol-1-yl)-1,1′-biphenyl]-4-yl)-1-phenyl-1 H -benzo[ d ]imidazole (INDY) has been designed and synthesized for solution-processed PHOLEDs. A hole-transporting indole conjugated dibenzofuran scaffold and an electron-transporting benzimidazole unit were orthogonally connected with incorporation of a 2,4′-biphenyl bridge, which endows a balanced bipolar charge transfer distribution and appropriate triplet energy level (>2.6 eV). The twisted conformation of INDY also ensures good thermal/morphological stability with high T g (148 °C). The solution-processed green PHOLEDs achieved great device efficiencies with 27.33 cd/A and 12.26 lm/W at 7 V. Meanwhile, the red solution-processed PHOLEDs gained excellent performance with the maximum efficiencies of 17.20 cd/A, 9.82 lm/W, and 12.61%. In addition, all of the red devices presented excellent color stability with the same CIE coordinate as (0.65, 0.35) under varying dopant contents and operating voltages.